Field of the Invention
The present generally relates to image processing and, more particularly, to an image processing method and an image processing apparatus for generating print data based on input image data.
Description of the Related Art
When printed images are used as business documents, the quality level of characters is regarded as most important, so that it is necessary to print character images in high resolution. If such a high-resolution color image is to be processed, the amount of image data transferred to a printer increases. Further, a large processing load may be generated in the printer for storing and processing such image data.
To address this issue, there is a method in which a printer driver transfers multi-valued image data to the printer, and the printer then converts the multi-valued image data to low gradation image data. The printer thus forms an image on a printing medium based on the low gradation printing data. Such a method is advantageous in that the process to be performed by the printer driver can be performed by a plurality of printers in a common way.
Further, Japanese Patent Application Laid-Open No. 2003-508827 discusses a technique for separating input image data into data corresponding to a color image portion and data corresponding to black character image portion. Each data is then separately compressed and transferred, and the printer combines the processed data.
However, if the input image data is separated, and low-resolution processing is simply performed on each separated data, color may change at a boundary portion between the color image portion (i.e., an image portion) and the character portion. Image quality may thus be degraded. More specifically, a value of one pixel in a low-resolution color image portion is determined based on the values of a plurality of pixels included in a unit region of the input image data. In such a case, if the color image portion and the character portion are both included in the unit region, the determined value becomes different from the value of the original color image portion. If the printer then performs printing based on such data, the color changes at the boundary portion between the color image portion and the character portion, so that the image quality is degraded.